Investigations of amnesia have contributed to our understanding of the neurology of memory. Amnesia occurs in a variety of neurological conditions following damage to either of two regions of the brain: the diencephalic region surrounding the third ventricle and the medial temporal-lobe region. There appear to be important differences between the amnesic syndromes produced in these two cases, both with respect to the presence of concomitant deficits that interact with the expression of the memory disorders and with respect to the nature of the memory disorders themselves. There are other etiologies of amnesia in which the link to diencephalic or temporal-lobe regions is less clear. Notable among these is the amnesic syndrome that sometimes occurs following successful surgery for anterior communicating artery aneurysm. The neuroanatomical substrate of this amnesic syndrome has not been described; little is known about its relationship to diencephalic and temporal-lobe amnesias. The proposed research will address these issues by providing the first comprehensive neurological, psychiatric, and neuropsychological characterization of the sequelae of surgery for anterior communicating artery aneurysm. The protocol will include both patients who do and patients who do not develop an amnesic syndrome. The findings will permit us to compare and contrast this syndrome anatomically and behaviorally to other amnesic syndromes, and thereby to determine the nature of this amnesic disorder. We shall administer tests of memory and other cognitive capacities in order to evaluate the effects of non-mnemonic deficits (e.g., linguistic or attentional deficits) on the expression of this form of amnesia. Such findings will contribute to our knowledge of the neurological foundations of memory. Furthermore, the assessment of behavioral capacities outside the domain of memory permits us for the first time to evaluate the syndrome as a whole. This approach should contribute substantially to the clinician's ability to provide a more informed prognosis and program of care for such patients.